This invention relates to a group of novel nitrided cutting tool materials which are characterized by excellent wear and abrasion resistance. Such materials are formed upon the nitriding of various refractory metal alloys which are set out in this specification.
More specifically, the alloy base materials of our invention consist of the following in percentages by weight shown herein
A. ONE OR MORE METALS OF THE GROUP COLUMBIUM AND VANADIUM AND OPTIONALLY TANTALUM (HEREIN "Group I");
b. hafnium;
C. ONE OR MORE METALS OF THE GROUP MOLYBDENUM, TUNGSTEN, RHENIUM AND CHROMIUM (HEREINAFTER Group II); and
D. OPTIONALLY, ONE OR MORE OF THE METALS TITANIUM AND ZIRCONIUM.
The amounts of these various metals to employ in fabricating the useful nitrided materials vary as a function of composition as will be seen herein.
When both titanium and zirconium are not present in these alloy systems the alloy base consists essentially of
A. FROM 55% TO 92% Cb and/or V with up to one-half of the content thereof being replaceable by Ta;
B. FROM 5% TO 40% Hf; and
C. FROM 2% TO 40% OF THE Group II metals, provided, however, that maximum chromium content is 20%.
When the metal or metals titanium and zirconium are present in the alloy systems of this invention and when hafnium content is equal to or greater than the content thereof we find that the following compositional parameters provide useful cutting tool materials when nitrided:
A. FROM 55% TO 85% OF ONE OR MORE METALS OF THE GROUP Cb and V, with up to one-half of the content thereof being replaceable by Ta;
B. FROM 5% TO 35% HAFNIUM;
C. AT LEAST 5% OF Ti and/or Zr and wherein total hafnium, titanium and/or zirconium ranges from 10% to 40% with Ti and/or Zr being equal to or less than Hf content; and
d. from 2% to 40% of one or more of the metals Mo, W, Re and Cr but maximum chromium content being 20%.
When the optional metal or metals titanium and zirconium are present in these alloy systems and when hafnium content is less than the content thereof we find that the following compositional parameters provide useful cutting tool materials when nitrided:
a. from 40% to 88% of one or more metals of the group Cb, Ta, V;
b. from 5% to slightly less than 20% hafnium;
c. such an amount of titanium and/or zirconium wherein total Hf, Ti and/or Zr ranges from 10% to 40% with hafnium content being less than Ti and/or Zr; and
d. from 2% to 40% of one or more metals of Group II.
These tool materials have a nitrogen pick-up of at least 0.1 milligram per square centimeter of surface area. In the preferred embodiments hereof the nitrogen pick-up is at least 1.0 mg/cm.sup.2 of surface area, and more preferably greater than 5.0 mg/cm.sup.2.
Another aspect of our invention is directed to herein disclosed nitrided materials wherein up to 25% of the nitrogen is replaced by oxygen or boron or mixtures thereof.
In the present specification and claims, unless otherwise specifically noted, all compositional percentages are by weight.
We have found that the present nitrided materials are characterized by high surface hardness without accompanying brittleness and offer excellent utility as cutting tool materials.